1. Field of the Invention
The present invention relates to a method of cleaning surfaces of a substrate processed by a developing process which wets the surfaces of the substrate with a developer after exposure, and a developing apparatus for carrying out the method.
2. Description of the Related Art
A resist pattern forming process is one of semiconductor device fabricating processes. The resist pattern forming process spreads a photoresist over a surface of a semiconductor wafer (hereinafter, referred to simply as “wafer”) in a photoresist film, exposes the photoresist film through a mask of a predetermined pattern, and develops the exposed photoresist film to form a resist pattern. Generally, this resist pattern forming process is carried out by a resist-applying-and-developing system formed by combining an exposure apparatus, and a developing apparatus capable of forming a resist film and of developing the exposed resist film.
A developing process included in a series of processes forms a resist pattern by wetting a surface coated with a resist film of a wafer with a developer and leaving the wetted wafer stationary for a predetermined time to remove soluble parts of the resist film. Then, the wafer is subjected to a cleaning process to remove a dissolution product produced by the dissolution of the resist, and the developer from the surface of the wafer. A spin cleaning method, namely, a conventional cleaning method, supplies a cleaning liquid onto a central part of the rotating wafer, and spreads the cleaning liquid by centrifugal force to wash out the dissolution product and the developer by the cleaning liquid. The spin cleaning method, however, is incapable of completely removing the dissolution product. Such an insufficient cleaning effect of the spin cleaning method is not a problem when the component lines of the resist pattern are wide. However, the possibility of the residual dissolution product producing development defects increases with decrease in the width of the component lines of the resist pattern. For example, the spin cleaning methods needs to continue a cleaning operation as long as 60 s, which is a principal factor causing the reduction of throughput. Cost reduction competition has been intensified in the semiconductor industry in recent years, the improvement of the throughput of semiconductor device fabricating processes is an urgent necessity. Since the resist pattern forming process has many steps, it is desired to reduce the process times of the steps to the shortest possible times. It is hardly possible to ensure perfect cleaning because, in some cases, the dissolution product cannot be completely removed even if the wafer is cleaned for a long cleaning time.
FIG. 13 is a typical view of assistance in explaining a spin cleaning method. A wafer W is held on a spin chuck 1, and the spin chuck 1 is rotated. Then, a cleaning liquid R is poured through a nozzle 11 onto a central part of the rotating wafer W. The cleaning liquid R spreads over the surface of the wafer W in a cleaning liquid film. It is considered that particles P of a dissolution product remain in the interface between the flowing cleaning liquid film of the cleaning liquid R and the surface of the wafer W. In another word, it is considered that the flowing cleaning liquid R is unable to wet the surface of a pattern formed on the wafer W satisfactorily or that flowing velocity of the cleaning liquid R in the interface is decreased by some cause.
A cleaning method disclosed in Patent document 1 pours a cleaning liquid onto a central part of a rectangular substrate being rotated at a low rotating speed on the order of 200 rpm, blows nitrogen gas against the surface of the substrate immediately after pouring the cleaning liquid onto the substrate. A liquid pouring position, onto which the cleaning liquid is poured, on the substrate and a gas blowing position, onto which nitrogen gas is blown, on the substrate are shifted simultaneously from the central part of the substrate toward a peripheral part of the same. A cleaning liquid pouring operation is stopped upon the shift of the liquid pouring position to a position on an inscribed circle tangent to the sides of the substrate.
When nitrogen gas is blown onto the gas flowing position behind the liquid pouring position onto which the cleaning liquid is poured as the liquid pouring position is shifted radially, the flow of the cleaning liquid is disturbed by the nitrogen gas, and particles separated from the surface of the wafer W are unable to flow together with the cleaning liquid and remain on the wafer W. Although this known cleaning method is more effective than the spin cleaning method, this known cleaning method has difficulty in exercising a high cleaning effect.
Patent document 1: JP-A 2002-57088, Paragraphs 0047 and 0049